My strong advice is to not to buy anything from a company that uses cold calls.
The best way to deal with a cold call is to put the phone down. A more fun alternative is to say that you are not the right person to speak to but you will go and find the person they need to speak to. Then just put the phone on hold – the caller will soon give up.
You may wish to get your number blocked from being added to future mailing lists through the Telephone Preference Service.